A. Field of the Invention
This invention relates to methods and apparatus for machining tubular workpieces to form couplings, and more particularly, to a method and apparatus for machining a tubular workpiece to form an internally threaded coupling having a faced and chamfered end and a tapered and counterbored interior without reversing the direction of rotation of the workpiece or indexing into position plural machining tools.
B. Description of the Prior Art
Couplings, which are used to connect the threaded pipe or other tubular goods, have at least one chamfered and faced end and a threaded tapered bore. In order to protect the thread from damage, couplings are typically counterbored.
At Jo-Way Tool Company, couplings are presently machined from tubular stock with the use of numerically controlled machines, which include a chuck for supporting and rotating the tubular stock about its longitudinal axis and means for manipulating tools to machine the tubular stock to form the various surfaces of the coupling. The tool manipulating means includes a turret adapted to support and index into position a plurality of tools, and means for moving the turret axially and radially relative to the axis of the workpiece.
Conventionally, it requires at least three tools to machine a coupling; a tool for chamfering and facing the end of the tubular stock; a tool for tapering and counterboring the interior of the tubular stock; and a tool for threading the tapered interior of the tubular stock. The three tools are mounted at different stations of the turret of the numerically controlled machine. In operation, the first tool is indexed into position where it is manipulated to chamfer and face the end of the workpiece. The first tool is then moved clear of the workpiece and the turret is indexed to bring the second tool into position, whereupon the second tool is manipulated to taper and counterbore the interior of the workpiece. Then, the second tool is moved clear of the workpiece and the turret is indexed to bring into position the third tool, which is manipulated to thread the tapered interior of the workpiece. As is apparent from the foregoing, a substantial portion of the time involved in maching a coupling is devoted to moving the tool clear of the workpiece and indexing them to various positions. The time spent in clearing and indexing the tools is wasted because during such time the workpiece is not being machined. Moreover, the large motions required in clearing and indexing the tools increases the wear on the numerically controlled machine. Experience has shown that approximately 20% of all maintenance downtime on numerically controlled machines is directly attributable to turret indexing problems.
In an effort to overcome the above described shortcomings, a tool was developed that included a tool holder that supported a thread cutting tool and a cutting tool adapted to machine both the face and chamfer and the taper and counterbore. That tool did eliminate the need to clear and index the turret; however, because of tool design geometry, the cutting tool thereof was required to have a positive leading cutting edge that was adapted to cut in two directions. The positive leading cutting edge and the bidirectional feature of the prior tool required that the speed of rotation of the workpiece be reduced to the point where the time saved by not indexing the turret was less than the time added to the actual machining of the workpiece. Additionally, the cutting element of the prior tool was subject to excessive wear and frequent breakage, and consequently had to be replaced frequently, which resulted in poor quality work and excessive machine down time. The net result of the use of that tool was a decrease in efficiency and an increase in expense compared to that of the conventional method and apparatus.
It is therefore an object of the present invention to provide an improved method and apparatus for machining a coupling from a tubular workpiece wherein the workpiece is rotated in one direction of rotation about its longitudinal axis and the maching steps are performed without clearing and indexing into position multiple tools.